This invention relates to a porous ceramic body consisting of a large number of extremely fine cells and a method of manufacturing the same.
A porous ceramic body is widely accepted as a high temperature catalyst carrier required to have a resistance to acids and alkalis or a fine particle filter for trapping, for example, carbon particles carried along with exhaust gas.
A porous ceramic body known to date is of the honeycomb type. This ceramic honeycomb body has been manufactured by any of the following processes:
(i) extruding a ceramic material into the honeycomb form and later firing the extruded mass;
(ii) firing a bundle of a plurality of ceramic pipes;
(iii) applying a ceramic slurry to the surface of a sheet of paper, solidifying the mass into a flat board, superposing such flat boards to form a three-dimensional structure, and finally firing the superposed mass; and
(iv) applying a ceramic slurry into the pores of polyurethane foam and firing the whole mass after drying the foam coated with the slurry.
Any of the above-mentioned processes of manufacturing a ceramic honeycomb body characteristically comprises the step of forming a large number of passages having a rectangular, triangular, hexagonal or circular cross section in said ceramic body. The passages produced by any of the conventional processes have a width or diameter ranging from about 0.5 to about 1 mm. Insofar as the honeycomb shape is retained, reduction in the cross sectional area of said passage has been subjected to a certain limitation in respect of the manufacturing process.
Passages having a relatively large width or diameter resulting from the above-mentioned limitation have been accompanied with the drawbacks that a gas idly flows through the passage without bringing about any result; a honeycomb body used as a filter decreases in its filtering function; and a honeycomb body applied as a catalyst carrier has the disadvantage that the gas contact area is undesirably reduced. Where, however, it is attempted to reduce the cross sectional area of the passage for the object of preventing a gas from idly running through said passage, then the breathability of the honeycomb body drops, obstructing its original function. According to any of the aforementioned ceramic honeycomb-manufacturing processes, the passage has a smooth inner wall, thereby being handicapped by the drawback that where said ceramic honeycomb body is used to trap extremely fine particles, dusts and soots contained in a gas are hardly able to be trapped by the passage due to the smooth inner wall.
Another known porous ceramic body is a porous brick. This porous brick consists of a large number of cells having a smaller cross sectional passage area than that of the aforementioned ceramic honeycomb body and offers greater advantage than said ceramic honeycomb body as viewed from the standpoint of preventing the idle passage of a gas. Nevertheless, the porous brick is still accompanied with the drawbacks that its relatively large porosity gives rise to a decline in its mechanical strength; when used in an environment able to be subjected to a great load, the brick tends to be cracked; when applied as an exhaust-treating carrier ready to be shocked, the brick also tends to be cracked, and the broken pieces of brick sometimes tend to fall off.